Performance of Ultrasound in the Diagnosis Cohort O

ORIGINAL RESEARCH CONTRIBUTION
Performance of Ultrasound in the Diagnosis
of Appendicitis in Children in a Multicenter
Cohort
Manoj K. Mittal, MD, Peter S. Dayan, MD, MSc, Charles G. Macias, MD, MPH, Richard G. Bachur, MD,
Jonathan Bennett, MD, Nanette C. Dudley, MD, Lalit Bajaj, MD, MPH, Kelly Sinclair, MD, Michelle D.
Stevenson, MD, MS, Anupam B. Kharbanda, MD, MSc, for the Pediatric Emergency Medicine
Collaborative Research Committee of the American Academy of Pediatrics*
Abstract
Objectives: The objectives were to assess the test characteristics of ultrasound (US) in diagnosing
appendicitis in children and to evaluate site-related variations based on the frequency of its use.
Additionally, the authors assessed the test characteristics of US when the appendix was clearly visualized.
Methods: This was a secondary analysis of a prospective, 10-center observational study. Children aged
3 to 18 years with acute abdominal pain concerning for appendicitis were enrolled. US was performed at
the discretion of the treating physician.
Results: Of 2,625 patients enrolled, 965 (36.8%) underwent abdominal US. US had an overall sensitivity
of 72.5% (95% confidence interval [CI] = 58.8% to 86.3%) and specificity 97.0% (95% CI = 96.2% to
97.9%) in diagnosing appendicitis. US sensitivity was 77.7% at the three sites (combined) that used it in
90% of cases, 51.6% at a site that used it in 50% of cases, and 35% at the four remaining sites
(combined) that used it in 9% of cases. US retained a high specificity of 96% to 99% at all sites. Of the
469 (48.6%) cases across sites where the appendix was clearly visualized on US, its sensitivity was 97.9%
(95% CI = 95.2% to 99.9%), with a specificity of 91.7% (95% CI = 86.7% to 96.7%).
Conclusions: Ultrasound sensitivity and the rate of visualization of the appendix on US varied across
sites and appeared to improve with more frequent use. US had universally high sensitivity and specificity
when the appendix was clearly identified. Other diagnostic modalities should be considered when the
appendix is not definitively visualized by US.
ACADEMIC EMERGENCY MEDICINE 2013; 20:697–702 © 2013 by the Society for Academic Emergency
Medicine
From the Department of Pediatrics, The Children’s Hospital of Philadelphia, and Perelman School of Medicine, University of Pennsylvania (MKM), Philadelphia, PA; the Department of Pediatrics, Columbia University College of Physicians and Surgeons (PSD,
ABK), New York, NY; the Department of Pediatrics, Baylor College of Medicine (CGM), Houston, TX; the Division of Emergency
Medicine, Children’s Hospital Boston, Harvard Medical School (RGB), Boston, MA; the Department of Pediatrics, Alfred I. duPont
Hospital for Children (JB), Wilmington, DE; the Department of Pediatrics, University of Utah School of Medicine (NCD), Salt Lake
City, UT; the Department of Pediatrics, University of Colorado School of Medicine (LB), Denver, CO; The Children’s Mercy Hospital (KS), Kansas City, MO; the Department of Pediatrics, University of Louisville (MDS), Louisville, KY; and the Department of Pediatric Emergency Medicine, Children’s Hospital and Clinics of Minnesota (ABK), Minneapolis, MN.
*Members of the Executive Committee of the Pediatric Emergency Medicine Collaborative Research Committee of the American
Academy of Pediatrics: Marc Auerbach, MD, and Lei Chen, MD, Yale School of Medicine, New Haven, CT; Todd Chang, MD, Children’s Hospital Los Angeles, Los Angeles, CA; Andrea Cruz, MD, and Charles G. Macias, MD, Baylor College of Medicine, Texas
Children’s Hospital, Houston, TX; Denise Dowd, MD, Children’s Mercy Hospitals and Clinics and University of Missouri–Kansas
City School of Medicine, Kansas City, MO; Anupam B. Kharbanda, MD, Children’s Hospitals and Clinics of Minnesota, Minneapolis, MN; Prashant Mahajan, MD, University of Michigan, Detroit, MI; Lise Nigrovic, MD, Children’s Hospital Boston, Boston, MA;
David Schnadower, MD, Washington University School of Medicine, St. Louis, MO; and Rakesh D. Mistry, MD, and Joe Zorc,
MD, The Children’s Hospital of Philadelphia, Philadelphia, PA.
Received October 30, 2012; revision received January 29, 2013; accepted February 13, 2013.
Presented at the 2012 Pediatric Academic Societies Annual Meeting, Boston, MA, April 28–May 1, 2012.
The authors have no relevant financial information or potential conflicts of interest to disclose.
Supervising Editor: Sarah A. Stahmer, MD.
Address for correspondence and reprints: Manoj K. Mittal, MD; e-mail: [email protected].
© 2013 by the Society for Academic Emergency Medicine
doi: 10.1111/acem.12161
ISSN 1069-6563
PII ISSN 1069-6563583
697
697
698
Mittal et al. • PERFORMANCE OF US IN THE DIAGNOSIS OF APPENDICITIS IN CHILDREN
A
cute abdominal pain accounts for 5% to 10% of
all pediatric emergency department (PED) visits. Approximately one-third of children with
acute abdominal pain concerning for appendicitis will
be diagnosed with it, making appendicitis the most
common surgical emergency in children.1–3 The diagnosis of pediatric appendicitis can be difficult, with a substantial proportion misdiagnosed based on clinical
features and laboratory tests alone.4 Computed tomography (CT) has become heavily relied on in the evaluation of children with possible appendicitis.1,5 However,
because of increasing concern over the long-term
malignancy risk related to CT-associated ionizing radiation, its routine use is being reappraised.6–9 There is
increasing interest in the use of ultrasound (US) as the
primary imaging modality for establishing or ruling out
the diagnosis of appendicitis in children and reserving
CT as a secondary diagnostic modality.10–13 Recently,
investigators noted a trend toward increased reliance
on US and decreased use of CT for children with
appendicitis among large U.S. pediatric hospitals.14
The current literature on the test characteristics of
US for diagnosis of appendicitis is composed of mainly
single-center studies, where US has been found to
have varied sensitivity (78% to 100%) and specificity
(88% to 98%).4,5,13,15–22 US is well known to be operator-dependent, yet there is scant information about its
performance at centers using it infrequently.23 Additionally, two retrospective studies suggest that the test
characteristics of US appear to improve when
restricted to patients where the appendix was clearly
identified, but further data are needed in this
regard.24,25
We conducted this secondary analysis from a large
multicenter cohort to assess the test characteristics of
US in diagnosing appendicitis and to evaluate siterelated variations based on the frequency of US use.
Additionally, we assessed the test characteristics of US
when the appendix was clearly visualized.
METHODS
Study Design
This was a secondary analysis of a prospective, observational study of children with suspected appendicitis.6
The Pediatric Emergency Medicine Collaborative
Research Committee (PEM-CRC) reviewed and
approved the final study protocol. Each participating
site’s institutional review board (IRB) also approved the
study. Seven IRBs granted waivers of written informed
consent or assent. At the three remaining sites, we
obtained written consent from the guardians and assent
from patients 7 years or older.
Study Setting and Population
This study was conducted at 10 PEDs located in tertiary care pediatric centers. All are members of the
PEM-CRC of the American Academy of Pediatrics.
We removed data from one site prior to analysis as
its capture rate (proportion of eligible patients
enrolled) was below 40%. A second site did not contribute to this secondary analysis as no study subject
underwent US. The eight sites included were labeled
A to H. We enrolled study subjects from March 2009
through April 2010.
Study Protocol
We enrolled children 3 to 18 years of age who presented
to the ED with acute abdominal pain of <96 hours duration who were being evaluated for suspected appendicitis. “Suspected appendicitis” patients were defined as
those for whom blood tests, radiologic studies (CT and/
or US), and/or surgical consultation were obtained for
the purpose of diagnosing appendicitis. We excluded
patients with any of the following conditions: pregnancy,
prior abdominal surgery (e.g., gastrostomy tube, abdominal hernia repair), chronic gastrointestinal illness or
abdominal pain (e.g., inflammatory bowel disease,
chronic pancreatitis, chronic or recurrent appendicitis),
sickle cell anemia, cystic fibrosis, a medical condition
affecting the provider’s ability to obtain an accurate
history (e.g., language or developmental delay), or history of abdominal trauma within 7 days of evaluation.
Patients who had radiologic studies (CT or US) of the
abdomen performed prior to emergency department
(ED) arrival were also excluded. The detailed study procedures have been published previously, including those
related to training of site staff, patient enrollment, data
collection, and transmission to the central data management warehouse.26
Clinicians obtained US at their discretion, not per
study protocol. We abstracted data from the final US
reports by the respective attending radiologists and
determined whether appendicitis was present using key
words that were defined a priori. We defined a positive
US as the radiologist read of “appendicitis” or “perforated appendicitis” based on visualization of an abnormal
appendix with or without secondary signs and a negative
US as all other reported US results including “normal,”
“appendix not visualized,” “equivocal,” and “other.”
Outcome Measures
Final diagnosis of appendicitis was determined by
pathology, operative reports, or telephone follow-up.
For those who underwent appendectomy, we determined the presence or absence of appendicitis by
pathology reports. The presence or absence of perforation was determined from the attending surgeon’s written operative report. In cases where a nonsurgical
diagnosis was assigned, we contacted the family
approximately 2 weeks after the ED visit to assess for
resolution of signs and symptoms, visits to other sites of
care, and need for surgery. For families who could not
be contacted, we reviewed the medical record at the
study institution to assess for any revisits within
3 months of the initial ED visit to determine if the
patient underwent any abdominal imaging or operation
at that facility.
Data Analysis
We performed descriptive analysis to characterize the
study population. We calculated test characteristics of
US (sensitivity, specificity, positive predictive value
[PPV], negative predictive value [NPV], and likelihood
ratios [LRs]) with 95% confidence intervals (CIs) for the
entire cohort and for individual sites to assess site-
ACADEMIC EMERGENCY MEDICINE • July 2013, Vol. 20, No. 7 • www.aemj.org
Table 1
Demographic and Clinical Characteristics
Variable
Mean age,
yr (!SD)
Male
Clinical findings
<24 hours of
abdominal pain
History of
migration of
pain to RLQ
Presence of
maximal abdominal
tenderness in RLQ
Rebound tenderness
on exam
Abdominal guarding
on exam
Increase in pain
with walking
Appendicitis
Perforated
appendicitis
US Cohort
(N = 965)
Overall Cohort
(N = 2,625)
11 (!3.7)
10.8 (!3.8)
433 (44.8)
1,338 (50.9)
547 (56.6)
1,467 (55.9)
384 (39.8)
1,080 (41.2)
674 (69.8)
1,785 (68.0)
258 (26.7)
818 (31.2)
486 (50.3)
1,471 (56.1)
617 (64.0)
1,784 (68.0)
324 (33.6)
74 (22.8)
1,018 (38.8)
275 (27.0)
Data are reported as n (%) unless otherwise noted
RLQ = right lower quadrant; US = ultrasound.
related variations. Given that our data were obtained
from several hospitals, the assumption of independent
observations was not valid. We therefore used clustered
sandwich standard error estimates to calculate the CIs.
These standard errors allow for intrahospital correlation, relaxing the assumption that observations from the
same hospital are independent. For the main analysis,
we considered equivocal US results as test-negative. We
performed a sensitivity analysis to assess the effect of
both excluding and recategorizing equivocal cases as
test-positive. Additionally, we assessed US test performance in the subset of cases where the appendix was
clearly visualized.
RESULTS
Of the 2,625 patients enrolled, 965 (36.8%) underwent
abdominal US to evaluate for possible appendicitis and
were analyzed for this study. We present the patient
demographics, clinical characteristics, and outcomes in
the overall cohort and in those for whom US was
obtained in Table 1. US was performed at a median of
1.7 hours (interquartile range [IQR] = 0.9 to 2.8 hours)
after physical examination. The median time from US
examination to an operative procedure for those
patients with presumptive diagnoses of appendicitis
was 5.9 hours (IQR = 3.7 to 9.9 hours).
For all patients, US had a sensitivity of 72.5% (95%
CI = 58.8% to 86.3%), specificity of 97.0% (95%
CI = 96.2% to 97.9%), PPV of 92.5% (95% CI = 87.4% to
97.7%), NPV of 87.5% (95% CI = 84.3% to 90.7%), positive likelihood ratio (+LR) of 24.5 (95% CI = 15.6 to 38.3),
negative likelihood ratio (–LR) of 0.28 (95% CI = 0.24 to
0.34), and overall accuracy of 88.8% (95% CI = 85.9% to
91.7%) for diagnosing appendicitis.
699
When we considered equivocal radiology reads as
positive, sensitivity was 79.9% (95% CI = 64.4% to
95.5%), specificity 84.4% (95% CI = 76.4% to 92.4%),
PPV 72.1% (95% CI = 62.5% to 81.8%), and NPV 89.3%
(95% CI = 84.3% to 94.2%). Excluding the cases with
equivocal radiology reads resulted in sensitivity of
78.3% (95% CI = 62.1% to 94.6%), specificity 96.6%
(95% CI = 95.6% to 97.6%), PPV 92.5% (95% CI = 87.4%
to 97.7%), and NPV 89.3% (95% CI = 84.3% to 94.2%).
We assessed the variation in test characteristics of
US across sites based on the frequency of its use
(Table 2). Sites A, B, and C used US as the first-line
imaging modality 24 hours a day and used it for 89% to
94% of their enrolled patients. The sensitivity at these
sites varied from 69% to 86%, with a combined sensitivity of 77.7% (95% CI = 54.7% to 99.9%). At site D,
where US was available only during the day and used
in 51% of subjects, its sensitivity was 51.6% (95%
CI = 33.0% to 70.2%). The last four sites (E, F, G, and H)
used US infrequently (9% of cases), and at these sites,
the combined sensitivity was 35% (95% CI = 20.0% to
50.0%). The appendix was definitively identified in 56%
of cases at sites A, B, and C combined; in 25% at site D;
and in 26% at sites E, F, G, and H combined. Regardless of site, specificity of US varied little, between 96%
and 99%.
When we restricted the analysis to those cases where
the appendix was specifically identified and classified as
normal or abnormal (469 cases, 48.6% of the total
cohort), we found an overall sensitivity of 97.9% (95%
CI = 95.2% to 99.9%), specificity 91.7% (95% CI = 86.7%
to 96.7%), PPV 92.5% (95% CI = 87.4% to 97.7%), NPV
97.7% (95% CI = 94.7% to 99.9%), +LR 11.8 (95%
CI = 7.7 to 18.2), and –LR 0.02 (95% CI = 0.009 to 0.05).
Table 3 shows the variation in test characteristics of US
across sites in this specific cohort. The sensitivity of US
remained at least 94% at all sites.
DISCUSSION
In this large multicenter study, we noted that use of US
varied substantially among the participating children’s
hospitals; overall US sensitivity was low, but was generally higher at sites using it more frequently. Sites that
used US as the primary imaging modality more
frequently visualized the appendix. All sites achieved
consistently high sensitivity when the appendix was
clearly visualized.
Imaging with US or CT has become routine for most
children undergoing diagnostic evaluation for appendicitis, with some believing that appendectomy should not
be undertaken without imaging to confirm the clinical
suspicion.10 A 2006 study found US of the appendix to
increase diagnostic accuracy, alter management, and be
more sensitive and specific than clinical impression,
either alone or in conjunction with laboratory results.4
There is increasing interest in the use of US for appendicitis, but its use appears limited by concerns related
to variable operator experience and overall performance.23 As our study shows, centers with more experience with, and reliable access to, US for children use
the modality more frequently. This is also reflected in
the findings of a recent study that showed that even
700
Mittal et al. • PERFORMANCE OF US IN THE DIAGNOSIS OF APPENDICITIS IN CHILDREN
Table 2
Variation in Use and Test Characteristics of US Across Sites
Site, n
US
Performed,
n (%)
Pattern of Use
of US/AvailabilityPattern of Use
A, 291
259 (89)
B, 240
225 (94)
C, 269
249 (93)
D, 223
114 (51)
E, F,
G, H,
1,308
118 (9)
24 hours a day/first-line
test
24 hours a day/first-line
test
24 hours a day/first-line
test
Daytime hours/used for
50% of patients
Daytime hours/infrequent
use
Prevalence,
%
Sensitivity,
%
(95% CI)
Specificity,
%
(95% CI)
+LR
(95% CI)
–LR
(95% CI)
44
86 (78–92)
97 (93–99)
30.9 (11.8–81.7)
0.14 (0.09–0.22)
41
73 (63–82)
96 (91–99)
19.3 (8.1–46.0)
0.28 (0.19–0.39)
26
69 (56–80)
96 (92–98)
18.2 (8.6–38.3)
0.32 (0.22–0.46)
27
52 (33–69)
98 (91–100)
21.4 (5.2–87.8)
0.49 (0.34–0.71)
17
35 (25–50)
99 (94–100)
27.2 (8.5–86.9)
0.56 (0.43–0.72)
+LR = positive likelihood ratio; –LR = negative likelihood ratio; US = ultrasound.
Table 3
Variation in Use and Test Characteristics of US Across Sites: Analysis Restricted to Cases Where Appendix Was Visualized and
Specifically Classified as Normal or Abnormal
Site, N
who had
US
Pattern of Use of
US-Availability/Pattern
of Use
A, 259
24 hours a day/first-line
test
24 hours a day/first-line
test
24 hours a day/first-line
test
Daytime hours/used for
50% of patients
Daytime hours
/infrequent use
B, 225
C, 249
D, 114
E,F,G,
H, 118
Prevalence of
Appendicitis,%
Appendix
Identified,
n (%)
Sensitivity,
%
(95% CI)
Specificity,
%
(95% CI)
+LR
(95% CI)
–LR
(95% CI)
52
190 (73)
100 (95–100)
96 (89–99)
22.8 (8.7–59.3)
0 (0-NaN)
66
106 (47)
97 (89–100)
86 (70–95)
6.9 (3.1–15.8)
0.03 (0.008–0.13)
41
114 (46)
96 (84–99)
90 (79–95)
9.2 (4.5–18.5)
0.05 (0.01–0.18)
61
28 (25)
94 (69–100)
82 (48–97)
5.2 (1.5–18.2)
0.07 (0.01–0.5)
22
31 (26)
100 (56–100)
96 (77–100)
24.0 (3.5–163.5)
0.00 (0-NaN)
+LR = positive likelihood ratio; –LR = negative likelihood ratio; NaN = not a number; US = ultrasound.
though the overall rate of use of CT in the United States
for evaluation of abdominal pain in children increased
every year from 1999 to 2007, the odds of undergoing
CT were significantly lower among patients who presented to a pediatric-focused ED with access to US.27
The overall sensitivity of US in our study is lower
than prior estimates, although the specificity is similar.
In a meta-analysis of studies published during the years
1986 to 2004, the authors found the pooled sensitivity
and specificity of US for diagnosing appendicitis in children of 88% (95% CI = 86% to 90%) and 94% (95%
CI = 92% to 95%), respectively.1 In a 2010 systematic
review, the authors reviewed studies published from
January 2000 to March 2007 and found that the sensitivity of US for diagnosing appendicitis in children varied
between 78 and 100% and the specificity from 88% to
98%.5,15–21 More recent reports have noted sensitivity of
91% to 99% and specificity of 97% to 98%.13,22 The
overall lower sensitivity that we obtained in our study
potentially provides a real-world estimate of test performance given the known interoperator variability in US
conduct. As our study was conducted only at pediatric
centers, US sensitivity may potentially be even lower at
sites with less pediatric experience.
The variable sensitivity across sites appears in large
part due to the varied ability to visualize the appendix.
Visualization rates of the appendix with US vary widely
in the published literature, from as high as 98% to as
low as 22%.15,24,28 Similar to other small studies, our
data show that US accurately confirms or excludes
appendicitis in cases where the appendix is clearly identified.24,25 Our study supports the position of other
authors that when US does not identify the appendix
clearly, clinicians need to consider other modalities
before diagnosing or excluding appendicitis.23,29,30
These diagnostic modalities may include repeat clinical
assessment; laboratory testing; admission for repeat
clinical exams; and/or US, CT, magnetic resonance
imaging, or discharge home with close follow-up.31,32
Factors that influence visualization of the appendix,
such as body mass index, need to be considered when
ordering US and should be the focus of future studies
that examine US utility.
Finally, the specificity of US was uniformly high at all
centers, supporting the clinical policy statement of the
American College of Emergency Physicians that US is,
across institutions, more useful to confirm acute appendicitis rather than exclude it.5 Our results suggest the
ACADEMIC EMERGENCY MEDICINE • July 2013, Vol. 20, No. 7 • www.aemj.org
need for sites to implement quality improvement practices to track hospital-specific US performance. The
threshold volume at which US performance improves
warrants further investigation.
LIMITATIONS
Although we enrolled patients from numerous geographical regions, enrollment occurred exclusively in
PEDs. US sensitivity may potentially be lower at community hospitals with less pediatric experience. Each
site followed its own rather than a standard study protocol for US image acquisition and interpretation, which
may have resulted in unaccounted-for differences across
sites. Radiologists were not blinded to clinical team
input or final outcomes. However, we used strict
abstraction rules to assess the final radiology readings.
We have no information about the experience of US
technicians or radiologists involved in the conduct and
interpretation of the studies; however, all the radiologists had pediatric training. Finally, patient-related factors such as age and body mass index, which can affect
the test characteristics of US, were not assessed.
CONCLUSIONS
Ultrasound had an overall lower sensitivity in diagnosing appendicitis in children in this multicenter cohort
than in previous reports. There was a large variation in
rates of identification of the appendix and sensitivity for
diagnosing appendicitis across sites, with lower rates at
centers that used ultrasound less frequently. Ultrasound
had high sensitivity and specificity, however, across all
sites when the appendix was clearly identified. Other
diagnostic modalities should be considered when US
does not identify the appendix clearly.
We thank all of the clinicians who enrolled patients into this study
and the research coordinators who greatly facilitated study completion. We are indebted to Michael C. Monuteaux, ScD, Division
of Emergency Medicine, Children’s Hospital Boston, Harvard Medical School, Boston, MA, for his help in statistical analysis of the
data.
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